Glass compression molding machine and machining chamber therefor

ABSTRACT

A molding die assembly includes an upper molding die and a lower molding die facing the upper molding die with provision for their alignment. The upper molding die includes an upper core, while the lower molding die includes a hollow cylinder and a lower core. The upper core has one of the molding surfaces that corresponds to a molding, while the lower core has the other molding surface corresponding to the molding. The lower core slides in the cylinder and defines a cavity in cooperation with the upper core. A clamping device applies a clamping force to the upper molding die and the lower molding die, and a compression device applies a compressive force between the upper core and the lower core. The clamping force is generated between the upper molding die and the lower molding die but not between the upper core and the lower core so that no clamping force is applied to the preform. Hence, if the upper platen and the lower platen are not parallel or if the volume of the preforms varies, surface accuracy and shape accuracy of the molding are still achieved.

BACKGROUND OF THE INVENTION

The present invention relates to a glass compression molding machine anda system employing same.

Previously, when an optical glass lens, for example, was molded, glasswhich had been melted and solidified was rough cut, subjected togrinding and so forth to form a glass preform of predetermined shape.Then, the preform was placed into a molding die assembly having precisemolding surfaces to compress the preform with heating, followed bygradually cooling the preform. The molding would then be ejected fromthe molding die assembly.

FIG. 1 illustrates the state of a molding die assembly of a conventionalglass compression molding machine before compression is performed. FIG.2 illustrates the state of the molding die assembly of the conventionalglass compression molding machine after compression has been performed.

Referring to the drawings, reference numeral 1 represents an upper core,2 represents a lower core, and 3 represents a cylinder disposed betweenthe upper core 1 and the lower core 2 to guide the vertical movement ofthe upper core 1. The upper core 1 includes a flange portion 1a forcontact with an upper heating plate (omitted from illustration), and acolumn portion 1b formed integrally with the flange portion 1a. A lowersurface 1c of the column portion 1b has a shape that corresponds to amolding 8.

The lower core 2 includes a flange portion 2a for contact with a lowerheating plate (omitted from illustration) and a column portion 2b formedintegrally with the flange portion 2a. An upper surface 2c of the columnportion 2b has a shape that corresponds to the molding 8 so that acavity 4 is formed in cooperation with lower surface 1c of the columnportion 1b.

The cylinder 3 is shaped to mate with the column portion 2b of the lowercore 2, the lower surface of the cylinder 3 coming into contact with theflange portion 2a of the lower core 2. The upper core 1 forms an uppermolding die 6, while the cylinder 3 and the lower core 2 form a lowermolding die 7.

With the upper molding die 6 separated from the lower molding die 7, arobot (omitted from illustration) places a preform 5 on the foregoinglower molding die 7. Then, an upper platen (omitted from illustration)is moved downwards closing the die cavity and clamping upper and lowermolding dies 6 and 7 together. The preform 5 is then heated andcompressed so that the molding 8 is obtained as shown in FIG. 2. Themolding 8 is cooled, and then the die assembly is opened by moving theupper platen upward. The molding 8 is removed by a robot or the like.

Therefore, each of the upper platen and lower platen (omitted fromillustration) is provided with a preform-injecting/molding-ejectingstation, a clamping/heating/compressing station and a gradual-coolingstation. Furthermore, independent clamping devices (omitted fromillustration) for heating, compressing and gradually cooling areprovided.

In compression, a compressive force is applied to the preform 5 in thecavity 4. The relative dimensions of the upper molding die 6 and thelower molding die 7 are set to provide a slight clearance d uponcompletion of the compression.

The upper molding die 6 and the lower molding die 7 of the foregoingtype, generally made of hard metal or ceramic, are used to mold glass athigh temperature and high pressure, resulting in adhesion of moltenglass to the surfaces of the upper core 1 and the lower core 2.Accordingly, the upper core 1 and the lower core 2 are covered with thinfilms to prevent the adhesion of the molten glass to their surfaces.

However, to the extent that the upper platen and the lower platen of theforegoing glass compression molding machine are not parallel, the uppermolding die 6 and the lower molding die 7 will not be properly aligned.As a result, the surface accuracy and the shape accuracy of the molding8 are reduced and, in particular, if the molding 8 is a glass lens, theresult is distortion of the optical axis of the glass lens.

FIG. 3 is a sectional view explaining the degree of parallelism betweenthe upper platen and the lower platen of the conventional glasscompression machine. FIG. 4 illustrates a conventional glass lensproduct.

In FIG. 3, reference numeral 1 represents an upper core, 2 represents alower core, 3 represents a cylinder, 6 represents an upper molding dieand 7 represents a lower molding die. Reference numeral 21 represents anupper heating plate to be brought into contact with the upper core 1,and 45 represents a lower heating plate to be brought into contact withthe lower core 2. The upper heating plate 21 is fastened to the upperplaten 9, while the lower heating plate 45 is fastened to the lowerplaten 10.

If the degree of parallelism between the upper platen 9 and the lowerplaten 10 of the foregoing molding die assembly is poor, clamping andcompressing cause a difference to occur between, for example, frontdistance H₁ and back distance H₂ between the upper heating plate 21 andthe lower heating plate 45.

Referring to FIG. 4, reference numeral 8 represents a glass lens moldinghaving thickness T. Reference numeral 8a represents a first opticalsurface and 8b represents a second optical surface respectively havingradii of curvature R₁ and R₂. If the degree of parallelism between theupper platen 9 (see FIG. 3) and the lower platen 10 is poor, distortione of the optical axis takes place, causing the thickness of theperipheral ends of the molding 8 to have different values t₁ and t₂.Therefore, sloping of the optical surfaces 8a and 8b expressed by Δt(=t₂ -t₁) is seen.

Where a plurality of upper molding dies 6 and lower molding dies 7 aremoved between the foregoing stations, the degree of parallelism betweenthe upper molding die 6 and the lower molding die 7 may also be poorand, as a result, the surface accuracy and the shape accuracy of themolding 8 become poor.

FIG. 5 is a cross-sectional view illustrating the degree of parallelismbetween the upper platen and the lower platen of a conventional glasscompression molding machine using plural die assemblies. Referring toFIG. 5, reference numeral 6 represents an upper molding die, 7represents a lower molding die, 8 represents a molding, 9 represents anupper platen, 10 represents a lower platen, 21 represents an upperheating plate and 45 represents a lower heating plate. In this case, aplurality of upper molding dies 6 are brought into contact with theupper heating plate 21 and a plurality of lower molding dies 7 arebrought into contact with the lower heating plate 45 in theclamping/heating/compression station.

If the preform 5 (see FIG. 1) has not been previously machined prior toplacement on the lower molding die 7, the volume of each preform 5 willvary by a degree of several percent. Differences in volume as betweendifferent preforms leads to a reduction in the degree of parallelismbetween the upper platen 9 and the lower platen 10. In other words, adifference between the front distance H₁ and the back distance H₂,between the upper heating plate 21 and the lower heating plate 45, isseen. As a result, one of the molding die assemblies is compressedexcessively, while the other is compressed insufficiently. In this case,thickness T₁ of the front molding 8 and thickness T₂ of the rear molding8 will be different from each other, thus reducing surface accuracy andshape accuracy.

In the foregoing conventional glass compression molding machine, theupper core 1 and the lower core 2 are covered with thin films to preventthe adhesion of molten glass to their surfaces. As a result, repeatedmolding operations will repeatedly subject the foregoing thin films to atemperature which is higher than 300° C., causing the thin films to beoxidized. Hence, the durability of the molding die assemblydeteriorates.

Therefore, the temperature of the upper molding die 6 and that of thelower molding die 7 cannot be detected accurately, and, accordingly, thecontrol of the temperature cannot be performed accurately.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a glass compressionmolding machine and a machining chamber therefor that are capable ofovercoming the foregoing problems experienced with the conventionalglass compression molding machine and capable of improving thedurability of a molding die assembly and performing accurate temperaturecontrol while maintaining good accuracy of surface and shape even if thedegree of parallelism between the upper platen and the lower platen ispoor and even if the preforms have different volumes.

In order to achieve the foregoing object, the glass compression moldingmachine according to the present invention provides a molding dieassembly, wherein an upper molding die and a lower molding die arealigned by a mating fit, i.e. a "spigot and socket" arrangement.

The upper molding die has an upper core, while the lower molding die hasa hollow cylinder and a lower core. The upper core has one of themolding surfaces that corresponds to the molding, while the lower corehas the other molding surface. The lower core slides in the cylinder andforms a die cavity in cooperation with the upper core.

Further, a clamping device for clamping the upper molding die and thelower molding die together and a compression device for generating acompressive force between the upper core and the lower core areprovided.

Therefore, closing of the die cavity is performed by moving the uppermolding die downward into contact with the lower molding die. Whenclamping, heating and compressing are performed, the upper core or thelower core is moved while maintaining the contact between the uppermolding die and the lower molding die. At this time, a preform placedinto the molding die assembly is deformed to produce a molding.

In the present invention, the clamping generates a force between theupper molding die and the lower molding die, but not between the uppercore and the lower core. Therefore, no clamping force is applied to thepreform. Hence, even if the degree of parallelism between the upperplaten and the lower platen is poor or the volumes of the preformsdiffer, the surface accuracy and the shape accuracy of the molding canbe maintained.

If the upper molding die has no cylinder, the cylinder of the lowermolding die is aligned with the upper core by a mating fit, i.e. aspigot and socket connection. If the upper molding die has a hollowcylinder and an upper core that slides in the cylinder, the cylinder ofthe lower molding die is aligned with the cylinder of the upper moldingdie by the mating fit.

Where a plurality of molding die assemblies and compression devices areprovided, the compression devices respectively and independentlygenerate compressive forces.

The upper molding die and/or the lower molding die is provided with ameans for supplying inactive gas to the area between the upper moldingdie and the lower molding die. In this case, the inactive gas issupplied through a gap formed between the core and the cylinder.Further, a nozzle ring may be disposed around the cylinder so as tosupply the inactive gas through a nozzle formed between the cylinder andthe nozzle ring.

Therefore, oxygen can be purged from the die cavity by displacement bythe inactive gas. The inactive gas forms a barrier around the moldingdie assembly, so that the ambient air does not enter the die cavity. Asa result, the oxidation of the thin film applied to the surfaces of thecores, by contact with oxygen, can be prevented and the durability ofthe molding die assembly is improved.

Temperature sensors are embedded in the cylinders, and plural heatingmeans are disposed on the outer surfaces of the cylinders andindependently controlled for each of the molding die assemblies inaccordance with the temperatures detected by the temperature sensors.Therefore, the temperature of each core can be maintained at anarbitrary level at each station, and accordingly, accurate temperaturecontrol can be achieved.

The chamber housing the glass compression molding apparatus, includingthe molding die assembly composed of the upper molding die and the lowermolding die, has a sealed casing and defines aclamping/heating/compressing station, a gradual-cooling station, and apreform-injecting/molding-ejecting station for the molding die assembly.

A shutter is provided in the casing to selectively open or close accessto the preform-injecting/molding-ejecting station. Further, a firstinactive-gas supply means and a second inactive-gas supply means areprovided, the first inactive gas supply means supplying inactive gas tothe area between the upper molding die and the lower molding die. Thesecond inactive gas supply means directly supplies inactive gas into thecasing.

A high-level non-oxygen area, in which the concentration of oxygen islow, is formed around the molding die assembly in the molding chamber,while a low-level non-oxygen area, in which the concentration of oxygenis somewhat higher, is formed in the remaining portion of the chamber.Therefore, even if the shutter is opened, oxidation of the thin film dueto its contact with oxygen can be prevented. As a result, the durabilityof the molding die assembly is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The structures and features of the invention will be apparent from thefollowing description taken in connection with the accompanying drawingswherein:

FIG. 1 is a cross-sectional view of a molding die assembly of aconventional glass compression molding machine before compression isperformed;

FIG. 2 is a cross-sectional view of the molding die assembly of theconventional glass compression molding machine of FIG. 1 aftercompression has been performed;

FIG. 3 is a cross-sectional view illustrating parallelism between anupper platen and a lower platen of the conventional glass compressionmolding machine of FIG. 1;

FIG. 4 is a side view of a glass lens;

FIG. 5 is a cross-sectional view illustrating parallelism between theupper platen and the lower platen in a conventional glass compressionmolding machine with plural die assemblies;

FIG. 6 is a cross-sectional view of a molding die assembly of a glasscompression molding machine according to a first embodiment of thepresent invention before compression is performed;

FIG. 7 is a cross-sectional view of the molding die assembly of theglass compression molding machine of FIG. 6 after compression has beenperformed;

FIG. 8 is a cross-sectional view of a glass compression molding machineaccording to a second embodiment of the present invention;

FIG. 9 is a time chart for equal-compressive-force control according tothe second embodiment of the present invention;

FIG. 10 is a time chart for equal-compression-quantity control accordingto the second embodiment of the present invention;

FIG. 11 is a cross-sectional view of a glass compression molding machineaccording to a third embodiment of the present invention;

FIG. 12 is a cross sectional view taken along line I--I of FIG. 11;

FIG. 13 is a cross sectional view taken along line II--II of FIG. 11;

FIG. 14 is a cross sectional view illustrating a glass compressionmolding machine with a heating coil, according to the third embodimentof the present invention;

FIG. 15 is a cross-sectional view showing compression with the glasscompression molding machine according to the third embodiment of thepresent invention;

FIG. 16 is a cross-sectional view illustrating placement of the preformand removal of the molding from the glass compression molding machineaccording to the third embodiment of the present invention;

FIG. 17 is a cross-sectional view of a glass compression molding machineaccording to a fourth embodiment of the present invention;

FIG. 18 is a cross-sectional view illustrating placement of a preforminto the glass compression molding machine according to the fourthembodiment of the present invention;

FIG. 19 is a cross-sectional view illustrating the closed state of thedies of the glass compression molding machine according to the fourthembodiment of the present invention;

FIG. 20 is a cross-sectional view illustrating removal of a molding fromthe glass compression molding machine according to the fourth embodimentof the present invention;

FIG. 21 is a schematic view of a molding chamber in which an atmosphereof nitrogen gas is formed;

FIG. 22 is a schematic view of a machining chamber of the glasscompression molding apparatus according to a fifth embodiment of thepresent invention;

FIG. 23 is an enlarged cross-sectional view of an essential portion ofthe fifth embodiment of the present invention; and

FIG. 24 is a plan view of a preform-injecting/molding-ejecting stationaccording to the fifth embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT

Preferred embodiments of the present invention will now be described indetail with reference to the drawings.

Referring to FIG. 6, reference numeral 24 represents an upper core, 25represents a lower core that can be brought into contact with the uppercore 24 and withdrawn and 26 represents a lower cylinder that can bebrought into contact with a shoulder of the upper core 24, and that canbe separated from the same, the lower cylinder 26 guiding the verticalmovement of the lower core 25. The upper core 24 includes a flangedportion 24a for contact with an upper heating plate (omitted fromillustration) a column portion 24b formed integrally with the flangedportion 24a and having the same diameter as that of the lower cylinder26, and a projection 24c formed integrally with the column portion 24band having the same diameter as that of a column portion 25b (to bedescribed later) of the lower core 25. A lower surface 24d of theprojection 24c has a shape that corresponds to a molding 8.

The lower core 25 includes a flanged portion 25a for contact with acompression rod (omitted from illustration) and a column portion 25bformed integrally with the flanged portion 25a. An upper surface 25c ofthe column portion 25b has a shape that corresponds to the molding 8,forming a cavity 4 in cooperation with the lower surface 24d of theprojection 24c.

The lower cylinder 26 includes a flanged portion 26a for contact with alower heating plate (omitted from illustration) and a cylindricalportion 26b formed integrally with the flanged portion 26a. The lowercylinder 26 is mounted so that the end surface of the cylindricalportion 26b may be brought into contact with an annular shoulder of thecolumn portion 24b of the upper core 24 and withdrawn from the same. Thecylindrical portion 26b mates with the column portion 25b of the lowercore 25 slidably disposed therein, and has a large-diameter bore 26c atthe lower end of its inner surface. The large-diameter bore portion 26creceives the flange portion 25a of the lower core 25. In order to enablethe flange portion 25a to be moved upward in the large-diameter portion26c before and after the compression, a clearance d' is provided.

It should be noted that the upper core 24 forms an upper molding die 27,and the lower core 25 and the cylinder 26 form a lower molding die 28.

With the molding die assembly open, a robot (omitted from illustration)places a preform 5 on the lower molding die 28. Then an upper platen(omitted from illustration) is moved downward to close the die assemblyand the end surface of the column portion 24b of the upper molding die27 is brought into contact with the end surface of the cylindricalportion 26b. Then, the preform 5 is heated, and the compression rod thenpresses against the lower core 25 to move column portion 25b upwardalong the inner surface of the cylindrical portion 26b. As a result, thepreform 5 is compressed as shown in FIG. 7 so that a molding 8 isformed.

Then, the molding 8 is cooled, the upper platen is moved upward to openthe dies, and the molding 8 is removed by a robot or the like.

Both the upper platen and the lower platen (omitted from illustration)move between a preform-injecting/molding-ejecting station, aclamping/heating/compressing station and a gradual-cooling station.Furthermore, independent clamping devices (omitted from illustration)are provided at each station.

At the time of compression, compressive force is applied to the preform5 in the cavity 4. The dimensions are set so that a slight clearance d'remains between the downward end surface of the large-diameter portion26c and the upward end surface of the flange portion 25a at the time ofthe completion of the compression.

If the dies are clamped with a poor degree of parallelism between theupper platen and the lower platen, the shoulder of the column portion24b of the upper core 24 will contact the end surface of the cylindricalportion 26b of the lower cylinder 26. Therefore, the clamping force canbe received by the upper core 24 and the lower cylinder 26, with theresult that no clamping force is applied to the preform 5.

The compressive force for molding the preform 5 is not supplied from theupper platen or the lower platen but, rather, is supplied from thecompression rod. Moreover, the column portion 25b of the lower core 25is confined by and slides along the inner surface of the cylindricalportion 26b, thus ensuring good parallelism between the upper core 24and the lower core 25. As a result, the surface accuracy and the shapeaccuracy of the molding 8 is improved.

FIG. 8 is a cross-sectional view of a glass compression molding machineaccording to a second embodiment of the present invention whereinreference numeral 8 represents a molding, 9 represents an upper platen,10 represents a lower platen, 25 represents a lower core, 26 representsa lower cylinder, 27 represents an upper molding die, 28 represents alower molding die, and 29 represents two of four tie bars which guidevertical movement of the upper platen 9 relative to the lower platen 10.

An upper heating plate 21 is fixed to the upper platen 9 through aninterposed heat insulating ring 30a, while a lower heating plate 45 isfixed to the lower platen 10 through an interposed heat insulating ring30b. A pair of upper molding dies 27 and a pair of lower molding dies 28are shown disposed between the upper heating plate 21 and the lowerheating plate 45. It is preferable that the heat insulating rings 30aand 30b be made of a ceramic exhibiting low heat conductivity and thatthe area of contact of those rings with the upper platen 9, the upperheating plate 21, the lower platen 10 and the lower heating plate 45 beminimal.

A clamping device (omitted from illustration) is connected to the upperplaten 9 to move the upper platen 9 downward along the tie bars 29. As aresult, the molding die assembly is clamped with clamping force F₀, andthe preform 5 (see FIG. 6) is heated and compressed so that the molding8 is obtained.

Multiple cartridge heaters 48a are embedded in the upper heating plate21 and multiple cartridge heaters 48b are embedded in the lower heatingplate 45 to heat the upper heating plate 21 and the lower heating plate45 to a temperature of 500 to 600° C.

Where the molding die assembly is clamped with clamping force F₀ byoperating the clamping device, a tension force F_(o) ' (=F_(o) /4) isreceived by each tie bar 29 as a reaction.

A pair of ceramic compression extension rods 60a are disposed below thelower cores 25, respectively, and a pair of ceramic compression rods 60bare disposed below the compression extension rods 60a, respectively. Asa result, the upward movement of the compression extension rods 60a andthe compression rods 60b compresses the preforms 5 with compressiveforces F₁ and F₂, respectively. Although two compression rods 60b areprovided in this embodiment, one or four or more compression rods 60bmay be provided. It is preferable that the compression extension rods60a be made of ceramic to prevent radiation of heat from the lower core25.

The compression rods 60b are disposed at positions that correspond tothe positions of the cavities 4 so that the compression rods 60btransmit the compressive forces F₁ and F₂ from the compression devices(omitted from illustration). The compression devices operating on thecorresponding compression rods 60b are able to be independently operatedto allow for a difference in the volumes of the preforms 5 and tomaintain parallelism between the upper platen 9 and the lower platen 10.

The sum of the maximum values of the compressive forces F₁, and F₂ isset smaller than the maximum value of the clamping force F₀ as expressedby the following expression:

    F.sub.1 +F.sub.2 <F.sub.0

Further, the compression device connected to the compression rod 60b canbe operated in any one of the equal-compressive-force control mode, theequal-compression-quantity control mode, andequal-compressive-force/equal-compression-quantity switch control mode.

In the equal-compressive-force control mode, control is performed sothat the compressive force F₁ and the compressive force F₂ are equal:

    F.sub.1 =F.sub.2

, while the compression quantities C₁ and C₂ are unequal:

    C.sub.1 ≠C.sub.2

In the equal-compression-quantity control mode, on the other hand, thecompressive force F₁ does not equal the compressive force F₂ :

    F.sub.1 ≠F.sub.2

, while the compression quantities C₁ and C₂ are equal:

    C.sub.1 =C.sub.2

Reference numerals 49a and 49b represent passages for cooling-waterformed, respectively, in the upper platen 9 and the lower platen 10 tocool the upper platen 9 and the lower platen 10 to about 50° C. and toprevent a rise in the temperature due to heat transmitted or radiatedfrom the upper heating plate 21 and the lower heating plate 45.

In the operation of the glass compressing molding machine describedabove, when the preform 5 is placed in the lower molding die 28 in thepreform-injecting/molding-ejecting station, the upper platen 9 is moveddownward by the clamping device so that the dies are closed. As aresult, the end surface of the column portion 24b of the upper core 24and the end surface of the cylindrical portion 26b of the cylinder 26are brought into contact with each other. At this time, the lowersurface of the flange portion 26a of the cylinder 26 and the lowersurface of the flange portion 25a of the lower core 25 are positioned onthe same plane so that the compressive force F₁ and the compressiveforce F₂ do not act on the preform 5.

When the upper molding die 27 and the lower molding die 28 have beenmoved to the clamping/heating/compressing station, the upper molding die27, the lower molding die 28 and the preform 5 are heated by heattransmitted from the upper heating plate 21 and the lower heating plate45. The temperature at which the preform 5 can be deformed bycompression is higher than the glass transition point T_(g) of thepreform material by 50 to 100° C. or more. Since it is difficult toraise the temperature instantaneously from room temperature to atemperature higher than the glass transition point T_(g) by 50 to 100°C. or more, because of the molding cycle, thepreform-injecting/molding-ejecting station is preheated to a temperaturelower than the glass transition point T_(g) by about 50° C.

When a predetermined time (one to two minutes) has passed after movementof the upper molding die 27 and the lower molding die 28 to theclamping/heating/compressing station as described above, the compressionrod 60b is moved upwards. The compressive force F₁ and the compressiveforce F₂ applied to the compression rods 60b are made equal, as shown inFIG. 9. The preform 5 is gradually deformed until the compressionquantities C₁ and C₂ are maximum after tens of seconds have passed.Therefore, a difference in the volumes of the preforms 5 results in adifference in the thickness T (see FIG. 4) of the moldings 8.

Since the compression process is commenced after the end surface of thecolumn portion 24b of the upper core 24 and the end surface of thecylindrical portion 26b of the lower cylinder 26 have been brought intocontact with each other, inclination of the optical surface 8a relativeto 8b as shown in FIG. 4 can be prevented.

Since the compressive quantities C₁ and C₂ are different from each otherin this case, the thickness T of the moldings 8 varies. However,deterioration in the optical characteristics can be prevented.

If variations in the thickness T are to be avoided, as shown in FIG. 10,the compressive force F₁ and the compressive force F₂ must be controlleduntil the thickness T equals a target thickness. When the thickness T ofone of the preforms 5 reaches a target thickness (point M), thocorresponding rod 60b is locked to prevent its further upward movement.

The same compressive force F₁ is continuously applied to the compressionrods 60b. When the thickness T of the preform 5 reaches a target value(point N), the compression rod 60b is locked. When the compression rod60b is locked, the upper molding die 27 and the lower molding die 28 arein a state where they are completely closed. The absorption of thestress in the glass will naturally reduce its reaction. Therefore, thecompressive force F₁ and the compressive force F₂ are also reduced.

A third embodiment of the present invention will now be described.Referring to the drawings, reference numeral 11 represents an uppermolding die. The upper molding die 11 comprises an upper core 12 and anupper cylinder 13 surrounding the upper core 12. The upper core 12 issupported by the upper cylinder 13 at the top end thereof, while thelower surface of same has a shape that corresponds to the molding 8 (seeFIG. 8). The upper molding die 11 is supported by a cylindricalupper-molding-die holder 15.

The upper-molding-die holder 15 has an upper-molding-die fastening plate16 extending laterally, and is supported by a pair of upper rails 17.The upper rails 17 are disposed parallel to each other along an upperplaten (omitted from illustration). By sliding the upper-molding-diefastening plate 16 along the upper rails 17, the upper molding die 11can be moved along the upper platen. Reference numeral 20 represents abolt for fixing the upper-molding-die holder 15 to the upper-molding-diefastening plate 16.

The upper platen is provided with a clamping/heating/compressing stationand a gradual-cooling station. In the clamping/heating/compressingstation, for example, an upper heating plate 21 is fastened to the upperplaten.

To facilitate movement of the upper molding die 11 along the upperplaten, the upper rails 17 can be spaced from the upper heating plate 21by about 1 mm.

The upper cylinder 13 includes a temperature sensor 22 such as athermocouple embedded therein. Since the leading end of the temperaturesensor 22 is in contact with the upper core 12, the temperature of theupper core 12 can be detected. Further, a coil heater 23 is wound aroundthe upper-molding-die holder 15 to control the temperature of the uppermolding die 11. As a result, the upper molding die 11 can be preheatedat the preform-injecting/molding-ejecting station. It should be notedthat the temperature of the upper core 12 can be detected even if theleading end of the temperature sensor 22 is not in contact with theupper core 12.

Reference numeral 31 represents a lower molding die. The lower moldingdie 31 comprises a lower core 32, a cylindrical lower cylinder 33surrounding the lower core 32, a pair of semicircular rings 34 and 35formed by dividing an annular member into two sections, and aflange-like lower molding die retainer 36 integrally and radiallyextending from the lower end of the lower cylinder 33. The upper surfaceof the lower core 32 has a shape that corresponds to the molding 8. Thelower molding die 31 is supported by a cylindrical lower-molding-dieholder 38.

The lower-molding-die holder 38 has a lower-molding-die fastening plate39 extending laterally. The lower-molding-die fastening plate 39 issupported by a pair of lower rails 41. The lower rails 41 are disposedparallel to each other along a lower platen (omitted from illustration).By sliding the lower-molding-die fastening plate 39 along the lowerrails 41, the lower molding die 31 can be moved along the lower platen.Reference numeral 43 represents a bolt for fixing the lower-molding-dieholder 38 to the lower-molding-die fastening plate 39.

The lower platen is provided with a clamping/heating/compressingstation, a gradual-cooling station and apreform-injecting/molding-ejecting station. In theclamping/heating/compressing station, for example, a lower heating plate45 is fastened to the lower platen.

To facilitate movement of the lower molding die 31 along the lowerplaten, the lower rails 41 are spaced from the lower heating plate 45 byabout 1 mm.

The lower core 32 has a small-diameter portion 32a of a predeterminedlength, in the lower portion thereof, which is surrounded by thesemicircular rings 34 and 35. Therefore, the lower core 32 can be movedvertically by a distance corresponding to the length of thesmall-diameter portion 32a, that is, by 5 to 10 mm in this case.

Since the lower cylinder 33 has a temperature sensor 46 such as athermocouple embedded therein in such a manner that the leading end ofthe temperature sensor 46 is in contact with the lower core 32, thetemperature of the lower core 32 can be detected. Further, a coil heater47 is wound around the lower-molding-die holder 38 so that thetemperature of the lower molding die 31 can be controlled independentlyfrom the upper molding die 11. As a result, the lower molding die 31 canbe preheated at the molding-ejecting station. It should be noted thatthe temperature of the lower core 32 can be detected even if the leadingend of the temperature sensor 46 is not in contact with the lower core32.

In order to provide an atmosphere of inactive gas, for example nitrogengas, the upper core 12 has a longitudinal notch 52 of a size from 50 to100 μ, and the lower core 32 has a longitudinal notch 53 of a size from50 to 100 μ. Further, an annular gap of about 5 μ is formed between theupper core 12 and the upper cylinder 13 and the same is formed betweenthe lower core 32 and the lower cylinder 33.

The notch 52 is in registration with a passage in the upper heatingplate 21 which, in turn, is connected to a line 55, communicating with avacuum pump (omitted from illustration), for example a rotary pump, viaan exhaust valve 56. On the other hand, the notch 53 registers with apassage in the lower heating plate 45 for connection to a nitrogen gascylinder (omitted from illustration) via line 57 and a nitrogen gasinjection valve 58. It should be noted that using the vacuum pump may beomitted.

The surfaces of the upper molding die holder 15 and the lower moldingdie holder 38 that face each other and the surfaces of the uppercylinder 13 and the lower cylinder 33 that face each other are machinedto a flatness providing a hermetic seal when they are held between theupper heating plate 21 and the lower heating plate 45 and the clampingforce is applied.

In order to enable the upper molding die 11 and the lower molding die 31to be moved horizontally, provision is made for center alignment.Alignment is provided for by a tapered surface 33b formed on theexterior of the leading end of the lower cylinder 33. Center alignmentis also provided by a tapered surface 12a formed around the exterior ofthe leading end of the upper core 12 and a tapered surface 33a formedinside the leading end of the lower cylinder 33.

Therefore, when the clamping operation is commenced, the inner surfaceof the upper-molding-die holder 15 and the tapered surface 33b formed onthe leading end of the lower cylinder 33 are aligned with each other,followed by movement of the upper-molding-die holder 15 downward alongthe tapered surface 33b. As a result, an initial alignment is achieved.As the dies 11 and 31 move further together, the tapered surface 12aformed on the leading edge of the upper core 12 and the tapered surface33a formed on the leading portion of the lower cylinder 33 are alignedwith each other. As a result, the upper molding die 11 and the lowermolding die 31 become completely aligned.

Reference numeral 60 represents a compression rod which forces the lowercore 32 upward in the clamping/heating/compressing station to compressthe preform 51.

The operation of the glass compression molding machine described abovewill now be described.

In the preform-injecting/molding-ejecting station, the preform 51preheated to 300° C. is placed into the lower molding die 31 by a robot(omitted from illustration). The lower molding die 31 has been preheatedto about 400° C.

The lower molding die 31 is moved along the lower rails 41 into theclamping/heating/compressing station so that the upper molding die 11and the lower molding die 31 are positioned as shown in FIG. 11. There,the upper core 12 and the lower core 32 are respectively held in theupper-molding-die holder 15 and the lower-molding-die holder 38 isspaced from the upper heating plate 21 and the lower heating plate 45 byabout 1 mm. The holders 15 and 38 are, in turn, supported byupper-molding-die fastening plate 16 and the lower-molding-die fasteningplate 39.

FIG. 14 illustrates heating according to a third embodiment of thepresent invention. When the clamping operation is commenced, theforegoing center-aligning is performed so that the state shown in FIG.14 is realized. As shown in FIG. 14, the temperature of the upperheating plate 21 and that of the lower heating plate 45 are controlledat 500 to 600° C., while the lower molding die 31 is heated up from thepreheated state (400° C.) with heat transmitted from the lower heatingplate 45. The temperature set by the coil heaters 23 and 47 wound aroundthe upper-molding-die holder 15 and the lower-molding-die holder 38 israised from 400° C. to within a range of 500 to 600° C.

The area between the upper molding die 11 and the lower molding die 31is hermetically sealed simultaneously with the commencement of theclamping operation. When the exhaust valve 56 is opened and thenitrogen-gas injection valve 58 is closed, air present between the uppermolding die 11 and the lower molding die 31 is evacuated by a rotarypump (omitted from illustration) to produce a vacuum. When the exhaustvalve 56 is then closed and the nitrogen-gas injection valve 58 isopened, nitrogen gas is supplied to the space between the upper moldingdie 11 and the lower molding die 31. It should be noted that the vacuumobtained with the rotary pump can be omitted.

FIG. 15 illustrates compression by the glass compression molding machineaccording to the third embodiment of the present invention. When thetemperature of the upper core 12 and that of the lower core 32, detectedby the temperature sensors 22 and 46, have risen to the level at whichthe preform 51 (see FIG. 11) is thermally deformed, the compression rod60 is moved upwards and a controlled compressive force is applied to thepreform 51. As a result, the shape of the upper core 12 and that of thelower core 32 are accurately transferred so that a molding 59 isobtained.

FIG. 16 illustrates transfer of a preform to and from the glasscompression molding machine according to the third embodiment of thepresent invention. When the upper platen (omitted from illustration) hasbeen moved upwards and, accordingly, the dies have been opened, theupper molding die 11 (see FIG. 11) and the lower molding die 31 aremoved to the preform-injecting/molding-ejecting station. Thepreform-injecting/molding-ejecting station is provided with a projectionrod 61 for pushing the lower core 32 upward to provide easy access for arobot (omitted from illustration) to introduce the preform 51 and removethe molding 59. The lower core 32 is moved upwards by the projection rod61, until the upward movement of the lower core 32 is stopped by theflange portion 32b formed at the lower end of the lower core 32 cominginto contact with the semicircular rings 34 and 35. Then, the robotremoves the molding 59 from the lower molding die 31, followed byplacement of the next preform 51 for the next molding cycle.

The surfaces of the upper core 12 and the lower core 32 are covered withthin films to prevent the adhesion of molten glass. However, the thinfilms are frequently exposed to the temperature higher than 300° C., andaccordingly, the thin films tend to become oxidized as the moldingoperation is repeated, reducing the durability of the molding dieassembly. To prevent such oxidation the present invention suppliesnitrogen gas to the space between the upper molding die 11 and the lowermolding die 31 in the clamping/heating/compressing station, thusimproving the durability of the molding die assembly.

A fourth embodiment of the present invention will now be described withreference to FIG. 17, which is a cross sectional view of a glasscompression molding machine according to the fourth embodiment of thepresent invention, and wherein reference numeral 11 represents an uppermolding die. The upper molding die 11 includes an upper core 12 and anupper cylinder 13 that surrounds the upper core 12. The upper core 12 issupported by the upper cylinder 13 and has a lower surface of a shapecorresponding to the molding 8 (see FIG. 8). An upper nozzle ring 62 isdisposed around the upper molding die 11 to define an annular nozzle 63for forming a jet of inactive gas, for example, nitrogen gas.

The annular nozzle 63 is tapered to make the jet of nitrogen gas aconical shape. The vertical angle of the conical flow of the nitrogengas is made to be 60°. The gap of the annular nozzle 63 is about 1 mm atthe outlet, about 5 mm in the nozzle land portion, and about 5 mm at thejunction with an annular header which forms a reservoir acting toequalize the flow from the annular nozzle 63. The gap of the annularnozzle 63 is supplied with the nitrogen gas via a nitrogen-gas injectionvalve 72 and a throttle valve 73 provided on a line 71.

Further, the upper core 12 has a slit 52 of about 50 to 100 μ, while anannular gap of about 5 μ is formed between the upper core 12 and theupper cylinder 13. The slit 52 is connected to a line 55 forcommunication with a vacuum pump (omitted from illustration), forexample, a rotary pump, via an exhaust valve 56. The line 55 is providedwith an oxygen concentration meter 68. The vacuum established with thevacuum pump may be omitted.

The lower molding die 31 includes a lower core 32 and a lower cylinder33 that surrounds the lower core 32. The top surface of the lower core32 has a shape that corresponds to the molding. The lower cylinder 33has a large-diameter bore 33d at the lower end thereof, of a depth whichdefines a predetermined stroke for the lower core 32. The lower moldingdie 31 has a lower nozzle ring 64, forming an outer surface portionthereof, which defines an annular nozzle 65 for forming a jet ofnitrogen gas in cooperation with the leading end portion of the lowercylinder 33. The annular nozzle 65 is supplied with nitrogen gas via anitrogen-gas injection valve 72 and a throttle valve 74 provided in theline 71.

The annular nozzle 65 is tapered to make the flow of nitrogen gas aconical shape. The vertical angle of the conical flow of the nitrogengas is made to be 60°. The gap of the annular nozzle 65 is about 1 mm atthe outlet, about 5 mm in the nozzle land portion, and about 5 at thejunction with an annular header which forms a reservoir acting toequalize flow from the annular nozzle 65.

Further, the lower core 32 has a slit 53 of about 50 to 100 μ, while anannular gap (omitted from illustration) of about 5 μ is formed betweenthe lower core 32 and the lower cylinder 33. The slit 53 is connected toa line 57 for communication with a nitrogen-gas cylinder (omitted fromillustration) or the like via a nitrogen-gas injection valve 58.

The operation of a fourth embodiment of the present invention will nowbe described.

FIG. 18 illustrates placement of a preform into the glass compressionmolding machine according to the fourth embodiment of the presentinvention. FIG. 19 illustrates the positions of the dies of the glasscompression molding machine according to a fourth embodiment of thepresent invention when closed. FIG. 20 illustrates removal of a moldingfrom the glass compression molding machine according to the fourthembodiment of the present invention.

The upper molding die 11 (see FIG. 17) and the lower molding die 31 arepreheated to 350 to 650° C., and the preform 51 is preheated to 300 to600° C. Then, the preform 51 is placed in the lower molding die 31 by avacuum holder 78 of a robot (omitted from illustration). During thisoperation, nitrogen gas, that is continuously emitted from the annularnozzle 65, forms a conical barrier of nitrogen gas. Nitrogen gas iscontinuously emitted from the annular gap between the lower core 32 andthe lower cylinder 33 as well as from the slit 53.

The vacuum holder 78 passes through the barrier of nitrogen gas toaccess the lower molding die 31 to place the preform 51 into the lowermolding die 31, as illustrated in FIG. 18.

The lower molding die 31, into which the preform 51 has been placed, iscoupled with the upper molding die 11 as shown in FIG. 19 to close thedies 11 and 31. After closing, the exhaust valve 56 on the line 55 isopened to evacuate gas from the space defined by the upper cylinder 13,the lower cylinder 33, the upper core 12 and the lower core 32.

A small gap is formed along the parting line, at the juncture betweenthe upper cylinder 13 and the lower cylinder 33 and between the uppercore 12 and the lower core 32. As a result, an atmosphere of nitrogengas is formed around the upper cylinder 13 and the lower cylinder 33.Further, nitrogen gas is supplied, via the line 57, to the spacesurrounded by the upper cylinder 13, the lower cylinder 33, the uppercore 12 and the lower core 32. Therefore, when evacuating via the line55, that space is completely purged by nitrogen gas. Hence, airundesirably introduced at the time of introduction of the preform 51 isremoved.

The vacuum is maintained for several seconds, and then stopped. Sincethe space surrounded by the upper drum 13, the lower drum 33, the uppercore 12 and the lower core 32 is continuously pressurized with nitrogengas, no air can be introduced into the space. The nitrogen-gas injectionvalve 58 on the line 57 is closed until the opening to conserve nitrogengas, and opened again just before the dies are opened. Therefore, anatmosphere of nitrogen gas is formed in the space surrounded by theupper cylinder 13, the lower cylinder 33, the upper core 12 and thelower core 32 while the dies are opened.

After the dies have been fully opened, the molding 59 is removed by thevacuum holder 78 of a robot (omitted from illustration) as shown in FIG.20. Reference numeral 79 represents a line for connecting the vacuumholder 78 to a rotary pump (omitted from illustration), the line 79having a valve 80 disposed therein.

Although the third and the fourth embodiments prevent the oxidation ofthe films applied to the upper core 12 and the lower core 32, bysupplying nitrogen gas to the space between the upper core 12 and thelower core 32, it might be considered feasible to further prevent theoxidation of the thin films by enclosing clamping/heating/compressingstation within a closed machining chamber containing an atmosphere ofnitrogen gas. FIG. 21 is a schematic view of such a machining chamber inwhich such an atmosphere of nitrogen gas is formed, in which referencenumeral 51 represents a preform, 59 represents a molding, and 81represents a molding die assembly. Reference numeral 82 represents amachining chamber in which the clamping/heating/compressing station isformed, 82a represents a front chamber, 82b represents a rear chamber,and 83 represents a casing for sectioning and forming the foregoingmachining chamber 82, the front chamber 82a and the rear chamber 82b.

A partition door 84a is disposed between the ambient atmosphere and thefront chamber 82a, a partition door 84b is disposed between the frontchamber 82a and the machining chamber 82, a partition door 84c isdisposed between the machining chamber 82 and the rear chamber 82b, anda partition door 84d is disposed between the rear chamber 82b and theambient atmosphere.

The front chamber 82a, the machining chamber 82 and the rear chamber 82bcan be supplied with nitrogen gas, with the front chamber 82a, themachining chamber 82 and the rear chamber 82b being respectivelyprovided with throttle valves 85a to 85c for adjusting the quantity ofnitrogen gas supplied.

Since the molding die assembly 81 is conveyed with its dies coupled inthe foregoing case, the size of each of the foregoing partition doors84a to 84d cannot be reduced satisfactorily. Therefore, mixing willoccur between the ambient atmosphere and the atmosphere within the frontchamber 82a, between the front chamber 82a and the machining chamber 82,between the machining chamber 82 and the rear chamber 82b, and betweenthe rear chamber 82b and the ambient atmosphere, causing theconcentration of oxygen to be raised

If a cover (omitted from illustration) of the machining chamber 82 istemporarily removed to perform maintenance, the concentration of oxygenis raised, and, accordingly, several hours are required to lower theconcentration of oxygen to a predetermined level.

Accordingly, the concentration of oxygen around the molding die assembly81 can be lowered to 1000 ppm or lower in a short time to prevent a risein the concentration of oxygen at the time of injecting the preform 51or ejecting the molding 59.

A fifth embodiment of the present invention will now be described withreference to FIG. 22, which is a schematic view of the entire fifthembodiment, FIG. 23, which is an enlarged view of an essential portionthereof, and FIG. 24, which is a plan view of apreform-injecting/molding-ejecting station according to the fifthembodiment.

Referring to the drawings, reference numeral 86 represents an upperplaten, 87 represents a lower platen, symbol F represents aclamping/heating/compressing station disposed on the lower platen 87,G_(L) represents a left gradual-cooling station disposed adjacent to theclamping/heating/compressing station F, G_(R) represents a rightgradual-cooling station disposed adjacent to theclamping/heating/compressing station F, H_(L) represents a leftpreform-injecting/molding-ejecting station, and H_(R) represents a rightpreform-injecting/molding-ejecting station.

A clamping device (omitted from illustration) is disposed above theupper platen 86 to move the upper platen 86 downward to generateclamping force and to withdraw it upward.

In the clamping/heating/compressing station F, an upper heating plate 88is provided for the upper platen 86 and a lower heating plate 89 isprovided for the lower platen 87. In the left gradual-cooling stationG_(L), a left gradual-cooling upper heating plate 90 is provided for theupper platen 86, and a left gradual-cooling lower heating plate 91 isprovided for the lower platen 87. In the right gradual-cooling stationG_(R), a right gradual-cooling upper heating plate 92 is provided forthe upper platen 86, and a right gradual-cooling lower heating plate 93is provided for the lower platen 87.

Each of the upper heating plate 88, the lower heating plate 89, the leftgradual-cooling upper heating plate 90, the left gradual-cooling lowerheating plate 91, the right gradual-cooling upper heating plate 92 andthe right gradual-cooling lower heating plate 93 is a cartridge heaterthat is controlled to maintain the temperature at a level required toperform the molding. That is, the high-temperature upper heating plate88 and the high-temperature lower heating plate 89 are set to atemperature higher than the glass transition point T_(g) of the glassmaterial to be molded, while the left gradual-cooling upper heatingplate 90 and the right gradual-cooling upper heating plate 92 are set toa temperature lower than the glass transition point T_(g). Thedifference between the two temperature levels is about 100° C.

A left molding die 94 and a right molding die 95 are disposed formovement along the upper platen 86 and the lower platen 87. A pair ofthe left molding dies 94 and a pair of the right molding dies 95 areprovided at each of the front and the back of the glass compressionmolding machine to provide a twin-molding-type glass compression moldingmachine.

Both the left molding die 94 and the right molding die 95 has an uppermolding die 11 and a lower molding die 31. The upper molding die 11 andthe lower molding die 31 are allowed to close and separate from eachother with the parting line as the boundary. The upper molding die 11comprises an upper core 12, an upper cylinder 13 that surrounds theupper core 12, an electromagnetic induction coil 97 that surrounds theupper cylinder 13, and an annular upper nozzle plate 98 fastened to thelower end of the electromagnetic induction coil 97. The upper nozzleplate 98 is secured to an upper molding-die fastening plate 100 by abolt 99 or the like to hold the upper cylinder 13 and theelectromagnetic induction coil 97.

The upper core 12 has a lower surface with a shape that corresponds tothe molding 59, and is supported by the upper cylinder 13. The uppermolding-die fastening plate 100 is commonly employed as an integralsupport for all of the upper molding dies 11.

A pair of L-shape rails (omitted from illustration) projecting downwardsare provided on the lower surface of the left gradual-cooling upperheating plate 90 and the right gradual-cooling upper heating plate 92.The upper molding-die fastening plate 100 can be freely moved alongthese rails in the left gradual-cooling station G_(L) and the rightgradual-cooling station G_(R), to position the upper molding die 11.

Each of the lower molding dies 31 includes a lower core 32, a lowercylinder 33 that surrounds the lower core 32, an electromagneticinduction coil 102 that surrounds the lower cylinder 33, and a lowernozzle plate 103 fastened to the top end of the electromagneticinduction coil 102. The lower nozzle plate 103 is secured to a lowermolding-die fastening plate 105 by a bolt 104 or the like to hold thelower cylinder 33 and the electromagnetic induction coil 102.

The lower core 32 has a top surface with a shape that corresponds to themolding 59, and is supported by the lower cylinder 33 by a pin 108. Incontrast to the arrangement wherein the upper core 12 is fixed to theupper cylinder 13, the lower core 32 is able to slidably move withrespect to the lower cylinder 33. In order to achieve this, the pin 108penetrates the lower cylinder 33 horizontally. On the other hand, anelongated through hole 109 for the pin 108 is horizontally formed in thelower core 32. Although the lower core 32 is usually supported by thelower cylinder 33 through the pin 108, the lower core 32 can be pushedupwards by the length of the elongated through hole 109.

The lower molding-die fastening plate 105 is commonly employed as anintegral support for all of the lower molding dies 31.

The lower molding die 31 can be moved among the leftpreform-injecting/molding-ejecting station H_(L), the leftgradual-cooling station G_(L), the clamping/heating/compressing stationF, the right gradual-cooling station G_(R), and the rightpreform-injecting/molding-ejecting station H_(R). In order to move thelower molding die 31, molding-die conveyance devices 111 are disposed tothe left and to the right of the glass compression molding machine. Eachmolding-die conveyance device 111 has a pair of supporting rods 112capable of moving forward/rearward with respect to the lower molding die31.

The lower-molding-die fastening plate 105 is secured to the leading endsof the supporting rods 112. Therefore, the molding-die conveyance device111 supports and moves the lower molding die 31 among the leftpreform-injecting/molding-ejecting station H_(L), the leftgradual-cooling station G_(L), the clamping/heating/compressing stationF, the right gradual-cooling station G_(R), and the rightpreform-injecting/molding-ejecting station H_(R).

In order to generate clamping force, a clamping device is disposed abovethe upper platen 86 to move the upper platen 86 downward in the leftgradual-cooling station G_(L) or the right gradual-cooling station G_(R)and to align the upper cylinder 33 with the lower cylinder 33 in themanner previously described. As a result, an intermediate stop positioncan be formed temporarily.

A clamping device (omitted from illustration) is also disposed below theclamping/heating/compressing station F to push the lower core 32 upward.As a result, the preform 51 is compressed to form the molding 59.

The annular upper nozzle plate 98 is fastened to the lower end of theelectromagnetic induction coil 97 as described above so that nitrogengas of high purity is emitted from the annular nozzle 101 formed betweenthe upper nozzle plate 98 and the upper cylinder 13 into the spacebetween the upper molding die 11 and the lower molding die 31.

The annular lower nozzle plate 103 is fastened to the top end of theelectromagnetic induction coil 102 as described above so that nitrogengas of high purity is emitted from the annular nozzle 106 formed betweenthe lower nozzle plate 103 and the lower cylinder 33 into the spacebetween the upper molding die 11 and the lower molding die 31.

The annular nozzles 101 and 106 are supplied with nitrogen gas viastainless steel lines 115, the flow of nitrogen gas being adjusted by athrottle valve 116. Since nitrogen gas is supplied to the space betweenthe upper molding die 11 and the lower molding die 31 as describedabove, the thin films formed on the surfaces of the upper core 12 andthe lower core 32 are not oxidized and the durability of the molding dieassembly is improved.

The upper platen 86, the upper heating plate 88, the lower heating plate89, the left gradual-cooling upper heating plate 90, the leftgradual-cooling lower heating plate 91, the right gradual-cooling upperheating plate 92, the right gradual-cooling lower heating plate 93, andthe molding-die conveyance device 111 and the like are all sealed withina casing 118 defining a machining chamber 119.

The machining chamber 119 contains an atmosphere of nitrogen gas.Nitrogen gas is supplied via the line 115 and the annular nozzles 101and 106 and is directly supplied into the machining chamber 119 via aline 121. The line 121 is provided with an electromagnetic valve 122 tocontrol the flow of nitrogen gas.

As a result, a high level area S_(H), in which the concentration ofoxygen is low (for example 100 to 1000 ppm=0.01 to 0.1), is createdadjacent to the annular nozzles 101 and 106 in the machining chamber119, and low level non-oxygen areas S_(L), in which the concentration ofoxygen is high (for example 1 to 0.1), are created in the other portionsof the machining chamber 119 as shown in FIG. 23. Symbol S_(A)represents an atmospheric area in which the concentration of oxygen is21%.

A portion of the casing 118 that corresponds to the leftpreform-injecting/molding-ejecting station H_(L) and a portion of thesame that corresponds to the right preform-injecting/molding-ejectingstation H_(R), for example, the ceiling portion of the casing 118 abovethe left preform-injecting/molding-ejecting station H_(L) and that abovethe right preform-injecting/molding-ejecting station H_(R), are providedwith a shutter 123. The shutter 123 is opened only when the preform 51is introduced or the molding 59 is removed. Therefore, the casing 118has a hole 131, the diameter of which is slightly larger than that ofthe vacuum holder 78 of a robot (omitted from illustration). The hole131 can be opened/closed by moving the shutter 123 in the directiondesignated by an arrow F shown in FIG. 24.

Since the pressure in the casing 118 is higher than that of the ambientatmosphere, the ambient atmosphere does not enter the casing 118 throughthe hole 131 at the time of opening the shutter 123. Therefore, even ifthe shutter 123 is opened, the concentration of oxygen in the high levelnon-oxygen area S_(H) is not raised.

The electromagnetic valve 122 in the line 121 and the throttle valve 116in the line 115 are opened prior to the commencement of molding tointroduce nitrogen gas. After a predetermined time has passed, theelectromagnetic valve 122 is closed. The electromagnetic valve 122 isused at the time of commencing the operation and is capable of supplyinga large quantity (for example, about 10 to 20 l/min) of nitrogen gas. Onthe other hand, the throttle valve 116 is always slightly open to supplya small quantity (for example, about 0.5 to 1 l/min per each of theannular nozzles 101 and 106) of nitrogen gas.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the preferredembodiments can be changed in the details of construction and in thecombination and arrangement of parts without departing from the spiritand the scope of the invention.

What we claim is:
 1. A glass compression molding apparatus comprising:(a) an upper heating plate; (b) an upper molding die including an upper flange portion for contact with said upper heating plate and, depending from said upper flange portion, an upper cylindrical portion which has a lower annular surface surrounding an upper cylindrical core, said upper cylindrical core having a lower endface with one of a pair of mating molding surfaces formed in and coextensive with said lower endface; (c) a lower heating plate for, in cooperation with said upper heating plate, heating a glass preform to a temperature suitable for molding; (d) a lower molding die forming a molding die assembly with said upper molding die, and including:(i) a lower hollow cylinder defining an interior bore of constant diameter which receives said upper cylindrical core with a mating fit, and having an upper annular surface for forming a mating fit with said lower annular surface; (ii) a lower flange, for contact with said lower heating plate, depending from a lower end of said lower hollow cylinder, opposite said upper annular surface; and (iii) a lower core which is slidably mounted in said interior bore for reciprocating movement relative to said hollow cylinder and said upper molding die, said lower core having an upper endface defining the other of said pair of mating molding surfaces; (e) clamping means for clamping together said upper molding die and said lower hollow cylinder to fix the position of said upper cylindrical core within said interior bore of said lower cylinder; and (f) compression means, operable independently of said clamping means, for driving said lower core upward within said interior bore, relative to the clamped upper molding die and lower cylinder, thereby generating compressive force between said pair of mating molding surfaces.
 2. A glass compression molding apparatus according to claim 1, wherein said lower hollow cylinder of said lower molding die is aligned with said upper cylindrical core by said mating fit.
 3. A glass compression molding apparatus according to claim 1, wherein said upper molding die further includes:an upper hollow cylinder, and wherein said upper cylindrical core is slidably mounted in said upper hollow cylinder, and wherein said lower hollow cylinder of said lower molding die is aligned with said upper cylinder of said upper molding die by said mating fit.
 4. A glass compression molding apparatus according to claim 1, comprising a plurality of sets of paired said upper and lower molding dies and said compression means, each of said compression means independently generating a compressive force.
 5. A glass compression molding apparatus according to claim 1 further comprising means for supplying inactive gas to a region between said upper molding die and said lower molding die.
 6. A glass compression molding apparatus according to claim 5, wherein said upper molding die further comprises an upper hollow cylinder, and said upper cylindrical core is slidably mounted in said upper hollow cylinder and wherein said inactive gas is supplied through a notch formed between the core and the cylinder of at least one of said upper and lower molding dies.
 7. A glass compression molding apparatus according to claim 5 further comprising a nozzle ring that surrounds said lower hollow cylinder and wherein said means for supplying inactive gas comprises a nozzle formed between said cylinder and said nozzle ring.
 8. A glass compression molding apparatus according to claim 3 further comprising:(a) temperature sensors embedded in said cylinders; and (b) heating means disposed on the outer surface of each of said cylinders and controlled in accordance with the temperatures detected by said temperature sensors.
 9. A glass compression molding apparatus according to claim 1, wherein said upper flange portion, said upper cylindrical portion and said upper cylindrical core of said upper molding die are integral, being formed as a single piece.
 10. A glass compression molding apparatus according to claim 9 wherein said lower hollow cylinder and said lower flange of said lower molding die are integral, being formed as a single piece.
 11. A glass compression molding apparatus according to claim 1 wherein said lower hollow cylinder and said lower flange of said lower molding die are integral, being formed as a single piece.
 12. A glass composition molding apparatus according to claim 1 further comprising:upper and lower platens, said lower platen supporting said lower heating plate through at least one heat insulating element and said upper platen bearing against said upper heating plate through at least one heat insulating element.
 13. A glass composition molding apparatus according to claim 1 further comprising:upper and lower platens, said lower platen supporting at least first and second lower heating plates and said upper platen supporting at least first and second upper heating plates, said first upper and lower heating plates defining a first station between said platens for receiving said upper and lower molding dies and said second upper and lower heating plates defining a second station between said platens for receiving said upper and lower molding dies. 